I am kinda new to DataStructure and I trying to write LinkedList, but I cannot figure out why my insert method does not work. If you have any suggestions to improve, please write to me
class Node:
def __init__(self, data):
self.item = data
self.ref = None
class LinkedList:
def __init__(self):
self.start_node = None
self.index = 0
def append(self, val):
new = Node(val)
if not self.start_node:
self.start_node = new
return
last = self.start_node
while last.ref:
last = last.ref
last.ref = new
self.index += 1
def insert(self, index, value):
start_counting = 0
start = self.start_node
while start_counting < index:
start = start.ref
start_counting += 1
NewNode = Node(value)
tmp = start.ref
start = NewNode
start.ref = tmp
def display(self):
ls = []
last = self.start_node
while last:
ls.append(last.item)
last = last.ref
return ls
The insert function is replacing the current node instead of linking it. I'll illustrate this with an example:
I have this linked list: 1 -> 2 -> 3 And I want to insert an element "4" in position 1 (the current number in position 1 is 2). The iterations will be:
start_counting = 0
start = self.start_node (node with value 1)
1st Iteration:
start_counting < 1 -> true
start = start.ref (node with value 2)
start_counting += 1 (actual count 1)
2nd Iteration:
start_counting < 1 -> false
start = (node with value 2)
After that the code continues as follows:
We create the new Node (4 in my example) and we do:
tmp = start.ref (which is 3)
start = NewNode (we are replacing the node completely, we are not linking the node with another) <- here is the error
start.ref = tmp (which in this case is 3)
To fix the error you should take in consideration two things:
The code would be something like:
def insert(self, index, value):
start_counting = 0
start = self.start_node
NewNode = Node(value)
if index == 0: # Handling the position 0 case.
NewNode.ref = start
self.start_node = NewNode
else:
while start_counting < index - 1: # Iterating until the previous node.
start_counting += 1
start = start.ref
NewNode.ref = start.ref
start.ref = NewNode
Tested with the following code and it is working:
a = LinkedList()
a.append(1)
a.append(2)
a.append(3)
a.insert(0, 4)
a.insert(1, 5)
print(a.display())
Linked list is not indexed, so you do not need to start from index=0. also for linked list, there are 3 insert methods, insert_to_first,insert_to_last or insert_to_any_position. You are implementing insert_to_any position.
def insert(self, index, value):
start_counting = 0
start = self.start_node
while start_counting < index:
start = start.ref
start_counting += 1
# so far no issue
NewNode = Node(value,None) # new Node accepts 2 args
# Let's write a linked list to visualize
# A->B->C-> adding_Node_Here ->D->E... make sure we dont lose ref to D when we inser
# after while loop, we end up start=C
NewNode.ref=start.ref # we keep the ref to D
start.ref=NewNode # now C refs to NewNode
self.index+=1 # again linked list is not indexed. "size" is better term
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